The invention relates to a thermal switch for particle-optical apparatus. In, for example, a cryo-TEM (transmission electron microscope), a sample 34 that is placed at an extremity 20 of a sample holder 7 can be maintained at, for example, the temperature of liquid nitrogen. There is a need to be able to inspect a sample at, for example, room temperature in a simple manner, without heating the microscope as a whole from the cryogenic temperature to room temperature. By using the thermal switch 40, this becomes possible. To this end, the thermal switch changes the thermal path between a cold source 22 in the apparatus and the extremity 20 of the sample holder 7, whereby, in one position, position 46.sup.a, a connection is made from the extremity 20 to the cold source 22, and, in the other position, position 46.sup.b, a connection is made to a portion 44 of the apparatus that is maintained at room temperature.